For touch screen applications, axis-intersect (AI) array projected capacitance sensing is the most popular touch sensing method due to its high optical clarity, durability and low cost. However, in detection of multi-touch, this art will result in ghost points and thereby cannot recognize the real points of the fingers touching on a capacitive touch panel.
FIG. 1 is a diagram showing a 2×2 ghost phenomenon of an XY-projected touch panel. When two fingers touches on the capacitive touch panel at an upper left point A and a lower right point D respectively, as shown in the right-side figure, or at an upper right point B and a lower left point C respectively, as shown in the left-side figure, a same capacitance variation scheme is induced, and there is no way to make difference for these two cases. Therefore, the control circuit of the touch panel cannot recognize the real points from the four points A, B, C and D.
In further detail, as shown in FIG. 2, ghost induced by a two-finger application involves two sets of coordinates. The capacitance variation in X-direction has two peaks at traces x1 and x2, and the capacitance variation in Y-direction has two peaks at traces y1 and y2. After excluding the combinations of coordinates with the same X-coordinate or Y-coordinate, two sets of coordinates remain as possible locations of the fingers, namely (x1y1, x2y2) and (x1y2, x2y1), of which one corresponds to the real points, and the other to ghost points. For multi-touch of three or more fingers, the number of ghost candidates will drastically increase. For example, as shown in FIG. 3, in the event of a three-finger application, there will be six sets of coordinates corresponding to possible real points, i.e., (x1y1, x2y2, x3y3), (x1y1, x2y3, x3y2), (x1y2, x2y1, x3y3), (x1y2, x2y3, x3y1), (x1y3, x2y2, x3y1), and (x1y3, x2y1, x3y2), of which five sets are ghost points.
Multi-touch is undoubtedly an important trend for the development of touch screens in future, and therefore it is desired a ghost resolution sensing method for improvement of the conventional AI array projected capacitance sensing.